1. Field of the Invention.
The present invention generally relates to the class of laboratory instruments identified as cell harvesters and, more particularly, to a novel cell harvester system, and method of operating the same, which includes, inter alia, improved cell wall washing, aspiration of liquid overflow from individual cells, and control of wash, aspirate, and overflow in individual sets of cells. An operator-programmable microprocessor may be employed to control a number of parameters in selected sequences.
2. Background Art.
In the field of medical and biotechnology research, there is a need to mark various test components of interest. These components may be cells containing antigens, antibodies or other factors. The most common marking methods use enzymes and radioactive labels. Once the cells are marked, they must be separated from the unmarked components, and then read or assayed. The ease of counting radioactivity facilitates this method of labelling. The newer methods of liquid scintillation counting increase the sensitivity of the method, while reducing the amount of radioactivity required. To further reduce the volume of reagents used, and thus the waste generated, the newer test methods are typically based on 96-well microplates using microliter test quantities.
The common method of harvesting from the microplates is to aspirate the test components from each of the wells on the plate through a filter substrate. The particulate matter, labeled with a radioactive material, is trapped by the filter, and unwanted components are washed away. The filter substrate is then radioactively counted to assay the test results.
A line of instruments, commonly referred to as cell harvesters, is used for the purpose of transferring components to the filter mat.
The present cell harvester designs originated from test tube-based protocols. Today, the trend is to the use of microplates using 96 wells holding up to 300 microliters each in an 8.times.12 array on 9 mm centers. For greatest efficiency, it is desirable to harvest all 96 wells simultaneously or by various segments, and do it automatically. This need presents new and different design challenges for the cell harvester. It now becomes necessary to seal 96 flow passages to the filter substrate. The lower volume of the microwells (300 microliters) means more wash cycles are required, if the past methods are to be used.
Conventionally, the well or tube is filled with wash solution to bring all of the components in contact with the wash solution. Then, the liquid contents are aspirated to the filter mat. The well or tube is refilled, and the process repeated several times. With only a 300-microliter volume limit, a number of consecutive wash and aspirate cycles are required to pass sufficient wash solution through the filter mat.
Present designs bring the wash buffer to the well in one line and aspirate to the filter mat with a second line. If the wash and aspirate lines open concurrently, the wash solutions enters the well only to be attracted to the aspirate line without washing the sidewalls of the wells, Thus, the operator must either manually raise and lower the aspirate tube in relation to the bottom of the well, or use the consecutive wash-aspirate cycles described above.
As test protocols become more sophisticated, it is not enough just to wash the particulate matter to the filter mat. There is a need to control the amount and type of wash solution, the rate of flow, and drying the filter mat at the end or in-between washes. In summary, there is a need to automatically and precisely control all of the parameters in cell harvesting needs.
Accordingly, it is a principal object of the present invention to provide a cell harvester system which controls separately or in concert the functions of wash, aspirate, and overflow in all wells or selected wells of a laboratory tray.
Another object of the invention is to provide means to fully wash the walls of such wells while simultaneously aspirating the wash solution from the wells.
An additional object of the invention is to provide means to aspirate any liquid which overflows a well without the liquid overflowing into adjacent wells.
A further object of the invention is to provide means for isolating a unique area of filter medium for a selected well.
Yet another object of the invention is to provide a microprocessor-based control for a cell harvester system.
Other objects of the invention, as well as particular features and advantages thereof, will be apparent from the following description and the accompanying drawing figures.